Baldur's Gate : The Sword Coast Chronicles : NWN2 Persistent World

Thinking about taking this as one of my epic feats on my Rogue/Warlock/DsM/SD toon. With Practiced Invoker and the spell progression from DsM, his caster level is only three levels behind a standard warlock, but his actual class level will only ever get as high as 15.

According to the wiki, the prerequisite for Extra Invocation is to be an "Epic Warlock." Does this mean I need to have a caster level of 21 or higher, or does it mean that it isn't accessible unless at least 21 of my levels are in the Warlock class...?

It's not available I think.

ah, sad day. Actually, as a follow-up question, some advice would be helpful from anyone versed in high level warlock play.

I have a build with HiPS and high AC but terrible Charisma, so any ability that allows a DC based save is to be avoided.

The four invocations I most want are Dark Premonition, Dark Foresight, Retributive Invisibility, and Otherworldly Leap. I thought the leap would be super fun, cut down on travel time, and allow me to get some distance against the occasional high spot check enemy. Which one of these invocations should I cut from the team and should I consider adding in something I haven't listed?

I find more useful Retributive invisibility and Dark Premonition (the 15 DR). About the other two I would choose Dark Foresight, but I would recommend you taking a look to Lure Shadow Demons: you summon 1-3 meatshields that will take the damage as you blast or backstabb. The bad point is that it only last 2 minutes and that it takes three round to be cast, but it is a great invocation.

A few things to note here.

Otherworldly leap has a cooldown, also, it don't always seem to work. Plus, the range is sort of limited. I tested it in the 100% rcr period, and I was sort of disappointing. You wan't it as a mobility tool, being able to jump distances, rivers, heights etc. And to this extend, it can work. But it seems unreliable when it comes to active use in combat. In other words... you may as well have UMD and get Dimensiondoor, if it's only for limited utility. If your moving around, and have to stand still, to cast a spell, that moves you a distance you could've outrun in the same time it took to cast the spell.... well.... Whats the point then?
SO yes, good for leaps to places you can't run to. Not good for active combat.

As for shadow demons. As already mentioned, it takes 3 or so rounds to cast the spell. After you cast it, it takes another round or so for the 0-3 demons to actually pop up. I had times when no demons showed, and when they did... well.... They are around lv 14 if I recall, which ain't bad mind you. But given everything else in the warlock armory is instant-cast, it is an element you need to consider.

Did not know that about Otherworldly Leap...I might just go get a dimension door wand then.

As for the demons, isn't that a spell that causes your alignment to shift when you use it?

there is no mechanical way to change your alignment any more (if there is it's a bug to be reported). Mechanical alignment change mechanics can be exploited, thus the ONLY way to change alignment is through documented RP with DM support/approval/intervention (as in the DM has to actually give you alignment points).